Security experts are urging Microsoft and Juniper to patch a year old IPv6 vulnerability so dangerous it can freeze any Windows machine on a LAN in a matter of minutes.

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Security experts are urging Microsoft and Juniper to patch a year old IPv6 vulnerability so dangerous it can freeze any Windows machine on a LAN in a matter of minutes.

Microsoft has downplayed the risk because the hole requires a physical connection to the wired LAN. Juniper says it has delayed a patch because the hole only affects a small number of its products, and it wants the IETF to fix the protocol instead.

The vulnerability was initially discovered in July 2010 by Marc Heuse, an IT security consultant in Berlin. He found that products from several vendors were vulnerable, including all recent versions of Windows, Cisco routers, Linux and Juniper’s Netscreen. Cisco issued a patch in October 2010, and the Linux kernel has since been fixed as well. Microsoft and Juniper have acknowledged the vulnerability, but neither have committed to patches.

The hole is in a technology known as router advertisements, where routers broadcast their IPv6 addresses to help clients find and connect to an IPv6 subnet. The DoS attack involves flooding the network segment with random RAs, which eats up CPU resources in Windows until the CPU is overloaded and a hard reboot is required. “For Windows, a personal firewall or similar security product does not protect against this attack, as the default filter rules allow these packets through,” explains Heuse.

Heuse became so frustrated with Microsoft’s refusal to fix the hole that he published his findings to the Full Disclosure mailing list on April 15. He notes that Microsoft has not even issued a security advisory warning users of the problem. Other Windows networking and security experts have also urged Microsoft to fix the problem, and sources have said that there are even employees inside Microsoft who have been trying to nudge the company to action.

Microsoft has little to say on the subject. “Microsoft is aware of discussions in the security community concerning a technique by which a Windows server or workstation on a target network may experience unprompted high resource utilisation caused by an attacker broadcasting malicious IPv6 router advertisements. The attack method described would require that a would-be attacker have link-local access to the targeted network, a situation that does not provide a security boundary,” a Microsoft spokesperson said.

However, experts aren’t buying it. The hole is “very easy to fix,” Heuse says, and Microsoft has a long history of addressing DoS holes on the local LAN that have far less of an impact. He points to Microsoft fixing a similar issue in 2008 of its implementation of IPv4. Meanwhile, Microsoft has also committed to fixing another issue he recently reported to the company which he describes as “a very minor vulnerability of detecting if a host is sniffing. It, too, is only possible on the local LAN.” His conclusion is that there is a political issue inside Microsoft where the “responsible team does not want to fix these kinds of issues anymore.”

Some Windows networking consultants are so concerned about the hole and Microsoft’s lack of interest in fixing it, that they have been warning users directly. “There is a serious Windows vulnerability for RA flooding as a denial-of-service attack on wired LANs. It only takes between 5 to 20 packets to CPU-bound every Windows 7 or Server 2008 machine on that subnet,” said Microsoft MVP Ed Horley, Principal Solutions Architect at Groupware Technology to attendees of the Rocky Mountain IPv6 Summit. “I have heard rumour it can also lock out Playstation 2 and Xbox consoles. With enough packets it requires a hard reboot to recover.”

Although several workarounds exist, each has a significant drawback. One is to turn off IPv6, which also disables new Microsoft technologies that rely on it, such as DirectAccess, a service that allows Windows 7 machines to have an always-on remote access connection to Windows Server 2008 R2 servers. Remote Access is touted as a money-saving option as it replaces the need for a separate VPN in Windows environments.